Oh boy, the furthest I've been in my life is North Yorkshire. Fun, heh...
As far as the UK goes:
Scotland - for the scenery
London - just to see what it's like
I doubt I'll ever get abroad, but if I could I'd love to go see:
Japan (or more specifically, Tokyo) - I imagine there's loads of weird and wonderful stuff there. And the place that spawned one of my fave metal bands has to be a good one, surely
USA - just want to see it, and maybe even meet some online friends
Norway - to see the fjords and valleys, for the scenery on the whole